1. Field of the Invention
The present invention relates to an apparatus and method for applying flexographic printing plates to the plate cylinders of printing machines.
It is essential that the flexographic plate be accurately positioned on each plate cylinder in order that images printed in different colours by different cylinders are in registration.
2. Description of Related Art
Canadian Pat. No. 975,217 issued to Chromax Limited on Sept. 30, 1975 shows a machine for such a purpose in which a flexographic printing plate is first positioned on a slide. The slide is then moved relatively to a printing cylinder and pressure sensitive adhesive on the reverse side of the flexographic plate causes it to stick to and wrap around the cylinder in registration.
The present invention provides an improved, compact and simple apparatus which first positions the flexographic printing plate on a register cylinder by means of register pins and then transfers the plate to a plate cylinder. The plate is retained on the plate cylinder surface magnetically or by an adhesive substance.
Specifically the invention relates to apparatus for mounting a flexographic plate in registration on a plate cylinder, the flexographic plate being provided with registration holes at one end thereof. The apparatus comprises: a register cylinder capable of controlled rotation and provided with a row of apertures to receive retractible registration pins at selected locations, means supporting a flexographic plate with the one end supported by the register cylinder and the registration holes engaged by registration pins, means for first rotating the register cylinder a precise amount whereby the flexographic plate is positioned for transfer to a plate cylinder, a movable plate cylinder support for receiving a plate cylinder at a predetermined rotational position, whereby the plate cylinder may abut the flexographic plate and register cylinder after the register cylinder has performed its first rotation, and means for further rotating the register cylinder when abutting the plate cylinder whereby the flexographic plate is transferred to the plate cylinder in registration.
In its method aspect the invention relates to a method for mounting a flexographic plate in registration on a plate cylinder by use of a register cylinder capable of controlled rotation and provided with a row of apertures to receive retractable registration pins at selected locations. The method comprises the steps of: positioning the flexographic plate with holes at one end engaging the pins in the register cylinder, rotating the register cylinder a precise amount, positioning the plate cylinder at a predetermined rotational position abutting the flexographic plate and register cylinder, retracting the registration pins and rotating both the register cylinder and plate cylinder whereby the flexographic plate transfers to the plate cylinder in registration.